Changes in the riparian zone of the lower Eygues River,France, since 1830 |
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| Authors: | G Mathias Kondolf Hervé Piégay Norbert Landon |
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| Institution: | (1) Department of Landscape Architecture, University of California at Berkeley, 202 Wurster Hall, Berkeley, CA 94720-2000, USA;(2) CNRS, UMR 5600 Environnement-Ville-Société, Site ENS-Lsh, 15 Parvis René Descartes, BP 7000, 69342 Lyon Cedex 07, France;(3) UMR 5600 Environnement-Ville-Société, Laboratoire Rhodanien de Géographie de I’Environnement, Université Lumière Lyon 2, 5 avenue Pierre Mendès-France, 69676 Bron cedex, France |
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| Abstract: | The riparian forests along braided rivers are dynamic, frequently rejuvenated by floods and channel changes, and thus dominated
by pioneer to middle stages of succession; they are sites of high biodiversity in some regions. The Lower Eygues River (drainage
area 1150 km2 in southeastern France) is such a braided river system with large alluvial forests dominated by Salix alba, Populus alba, and P. nigra. It was identified as a site of ecological interest by the EU under the Natura 2000 program. Such forests elsewhere in Europe have been identified as reference ecosystems. We documented the historical evolution
of this alluvial forest from detailed (1:2500 scale) early 19th C parcel maps, early 20th C topographic maps, aerial photography
from 1947 to 1996, and field surveys of topography and riparian vegetation in 1997–1998. Our results show that in 1830, the
channel was wide, aggraded, and agricultural pressure extended literally to the channel edge. With decline in the rural population
and reduced agricultural and grazing pressure in the catchment, erosion rates declined. Reduced sediment supply led to channel
narrowing and incision. This channel narrowing, coupled with reduced agricultural pressure along the banks, has allowed riparian
forest to colonize former active channel areas, especially within late 19th-century 20th century flood dykes. In recent decades,
aggregate mining, and clearing for recreation and agriculture have fragmented the forest. Thus, the alluvial forest of the
Lower Eygues is largely an artifact of changing human land-use over the past century, a context that should frame efforts
for preservation and restoration. |
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| Keywords: | historical analysis channel changes land use human impacts river restoration and conservation riparian vegetation |
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